Talking About Vaccines with Dr. Paul Offit: News Briefs – July 2016 – Nasal Spray Influenza Vaccine

Paul A. Offit, MD, talks about recent developments with the nasal spray influenza vaccine.

Transcript

Are there vaccines that children with allergies need to avoid?

Paul Offit, MD: Hi my name is Paul Offit. I’m talking to you today from the Vaccine Education Center at Children’s Hospital of Philadelphia. I want to talk to you about something that happened at the Advisory Committee for Immunization Practices (ACIP) meeting at the CDC (Centers for Disease Control and Prevention) on June 22 of 2016. At that meeting, the ACIP recommended that FluMist®, the live, attenuated influenza vaccine that has been given to children for many years, not be given for the upcoming 2016-2017 season. So why? How did we get to this point?

Remember a few years ago, FluMist® was recommended, frankly, as the preferred vaccine for children. It was recommended as preferred over the inactivated influenza vaccine, which was given as a shot because FluMist® appeared to work better; had a greater percentage of efficacy than did the inactivated vaccine; that because the vaccine virus of FluMist® reproduced itself at the nasal mucosal surface, that it had the capacity to drift, if you will, and that it maybe would have thought to have been better against strains where the match wasn’t perfect between what was in the vaccine and the strains that were circulating. Also, because it reproduced at the nasal mucosal surface, it induced a local immune response, therefore, more likely that when one was exposed to wild-type or natural virus that you would be less likely to transmit it from one person to another, and more importantly, I think, or most importantly, it’s just easier to give. I think it’s preferred by many children to get the FluMist® rather than to get the shot.

But over the last three years, FluMist® has dramatically underperformed the inactivated vaccine. In fact, this most recent year, the 2015-2016 season, the percent efficacy was estimated to be about three percent, which frankly is not better than placebo.

It’s unclear exactly what happened, but there are certainly reasons that have been proposed. One is that when you give the inactivated vaccine, for example, into the muscle, you know that you’re giving, for example, 15 micrograms of hemagglutinin per strain in the muscle. You know each of the 15 micrograms of hemagglutinin per strain will be taken up by local lymph nodes, processed and presented to the immune system.

When you give FluMist®, when you give the live-attenuated vaccine it’s not 15 micrograms of antigen or hemagglutinin per strain, it’s much much less than that because you depend on that vaccine virus reproducing itself at the nasal mucosal surfaces and essentially amplifying the amount of antigen that’s originally in that vial. So, I think you can assume that at some level replication wasn’t occurring at the nasal mucosal surface in a manner that was effective enough to generate large quantities of antigen.

So why is that? Why had it worked earlier but not later? I think one reason, and frankly the one that makes the most sense to me, is that when we went form the trivalent flu vaccine FluMist® to the quadrivalent vaccine of FluMist®, we had two B strains. I think it’s possible one of the B strains may have outcompeted the other three strains, so that you got a better immune response to one of the B strains, but not to the other three strains.

This has happened before. I mean if you look at rotavirus vaccines, sometimes one of the strains will, for example with Rotateq®, will reproduce itself better when you first get it. But again, you give multiple doses, so you have a chance then for those other strains to reproduce themselves better. Same with your oral polio vaccine. The type two polio strain actually was contained in the oral polio vaccine in a greater concentration than the other strains. So, I think you have to account for that when you give viruses, especially when it’s more than one virus, and it needs to reproduce itself in order to evoke a good immune response.

It’s hard to know whether this is the case. Certainly I think we can get answers to that by doing shedding studies to see whether or not one of the strains is outcompeting the other strains, whether we need to balance those strains differently. I’m optimistic FluMist® can come back into the United States, but only I think when we know those answers.

Hopefully that’s helpful. Thank you

Related Centers and Programs: Vaccine Education Center